Recently, as the amount of information significantly increases, strong demands have arisen for implementing a large-capacity information recording device. Element sizes of semiconductor memory devices are being extensively decreased in order to increase the capacity by increasing the packing density per unit area. For example, transistor wiring dimensions are being decreased within the range of a few nm to a few ten nm, so demands have arisen for implementing manufacturing techniques meeting this demand. Also, as hard disk drive (HDD) techniques, the development of various techniques such as perpendicular magnetic recording has been advanced to increase the density of a recording medium. In addition, a patterned medium has been proposed as a medium capable of further increasing the recording density and achieving a thermal fluctuation resistance of medium magnetization at the same time.
The patterned medium records one or a plurality of magnetic regions as one cell. To record one-bit information in one cell, individual recording cells must magnetically be isolated. Therefore, a general approach is to, e.g., isolate magnetic dot portions and nonmagnetic portions in the same plane by using the micropatterning techniques in the semiconductor manufacturing field. The patterned medium manufacturing methods include a top-down method and bottom-up method to be described below. The top-down method is a method of transferring a projection micropattern to a lower magnetic recording layer by using a projection pattern mask formed on the magnetic recording layer. On the other hand, the bottom-up method is a method in which a micropattern is formed on a substrate beforehand, a magnetic recording layer is deposited on the projection micropattern, and the recording layer material is traced into a projection shape, thereby obtaining an isolated pattern. Also, as a special method, a projection micropattern is formed on a magnetic recording layer, a nonmagnetic region is formed by irradiating the mask with high-energy ions and implanting the ions into a desired region, thereby selectively isolating the magnetic recording pattern.
As described above, in order to increase the recording density, it is necessary to form the above-mentioned micropattern on a substrate, and form a mask capable of corresponding to the pitch reduction of the projection pattern. Examples of the existing techniques meeting this demand are various lithography techniques using ultraviolet exposure or electron beam exposure. On the other hand, micropatterning using metal microparticles is available as a method capable of simply forming micropatterns with smaller dimensional variations.
A metal microparticle is a general term for microparticles having a diameter of a few nm to a few hundred nm, and is also called a nanoparticle or simply called a microparticle. When using metal microparticles on a substrate, the substrate is normally coated with a so-called dispersion in which the metal microparticle material is dispersed in a specific solvent, thereby obtaining a periodic pattern of the metal microparticles. Then, an independent projection pattern can be obtained on the same plane by using the metal microparticle coating film as a mask layer or underlayer. It is also possible to form a physical projection pattern on a substrate in advance, and artificially arrange a desired pattern by using the projection pattern as a guide.
Although metal microparticles are formed by various materials, microparticles using a noble-metal material are particularly chemically stable and have a high etching resistance. When using these microparticles as a projection pattern processing mask, it is possible to maintain the processing margin and reduce a dimensional conversion difference in the processed pattern. However, it is also possible to apply microparticles based on other oxide materials or compound materials.
Metal microparticles existing in a free space and dispersion tend to aggregate by receiving interactions from surrounding metal microparticles due to the Van der Waals force. To prevent this aggregation of the metal microparticles, therefore, a general designing/manufacturing guideline is to give a protective group having a polymer chain to the surface of each microparticle, thereby physicochemically isolating the microparticle from adjacent metal microparticles. In a micropatterning process using metal microparticles as masks, however, the protective group around each metal microparticle disappears due to plasma damage, so adjacent metal microparticles aggregate. Accordingly, a mask pattern changes on a substrate, and the dimensional variation of a transferred projection pattern worsens. The aggregation of the metal microparticles not only decreases the accuracy of the transferred pattern, but also behaves as a residue on the substrate. Therefore, unnecessary particles decrease the yield in a semiconductor manufacturing step, and particles forming a projection pattern deteriorate the head floating characteristic of a hard disk medium, and this worsens the HDI (Head Disk Interface) characteristic. Accordingly, suppressing the aggregation of microparticles is an important item in managing the yield of manufacturing steps. Also, as the dimensions of micropatterns are decreased, micropatterning is also required for mask materials, and this makes it necessary to transfer a projection pattern of narrow-pitch metal microparticles. On the other hand, as described previously, increasing the distance between microparticles in order to suppress the aggregation of the particles increases the inter-microparticle distance, i.e., the pattern pitch. Therefore, a method of suppressing aggregation without much increasing the inter-microparticle distance is necessary.
Furthermore, giving the protective group to the metal microparticle prolongs the manufacturing tact time and increases the cost. Accordingly, the protective group for suppressing the aggregation of the metal microparticles is desirably a material that does not much increase the inter-microparticle distance. In addition, the manufacturing method is desirably less expensive. However, a general conventional method is to give a polymer protective group when synthesizing metal microparticles, and this makes it difficult to meet the above-mentioned requirements at the same time as described above.
In a micropattern formation process using metal microparticles, therefore, it is desirable to secure narrow spacings, maintain the pattern arrangement accuracy, and increase the processing margin, in addition to suppressing the aggregation of the metal microparticles, so a manufacturing method capable of meeting all these requirements must be implemented. However, when forming a metal microparticle mask or projection micropattern by applying the conventional techniques, the above-described, trade-off problem arises, and this makes it extremely difficult to obtain a high-resolution projection pattern.